Metallic plug for stemming bore holes



Oct. 6, 1964 J. KARPovlcH 3,151,555

METALLIC PLUG FOR STEMMING BORE HOLES Filed July 6, 1961 2 Sheets-Sheet 2 INV EN TOR.

.Jo/1n Karp@ rich BMBM Oct.v6, 1964 J. KARPovlcH 3,151,556

METALLIC PLUG FOR STEMMING BoRE HOLES Filed July e, 1961 2 sheets-smv- 1 Exp/o/Ve 15 cha/'ge INVTOR. Jon Kar/oo w'c) United States Patent 3,191,556 METALLEC PLUG FOB. STEMMEN@ BORR HOLES .lohn Karpovich, Midland, Mich., assigner to The Bow Chemical Company, Midland, li/lich., a corporation of Delaware Filed .luly 6, 1961, Ser. No. 122,128

2 Claims. (Cl. N92- 24) The present invention is concerned with a metallic tamping plug suitable for use in bore holes and more particularly relates to a metal tarnping plug that can be pressfitted by explosive energy into firm contact with the wall of a bore hole.

Bore hole stemming is used to increase the connement on an explosive charge thereby increasing the effectiveness of the charge. Additionally, stemming a loaded bore hole helps to protect the explosive charge from accidental ignition as by l'lre or sparks and also aids in maintaining the charges in a predetermined relationship in the hole prior to detonation.

Ordinarily for vertical holes, as used in surface blasting, loose stemming materials such as drill churnings, sand, clay, small rocks, gravel and the like are employed. However, for underground blasting the bore holes ordinarily are not vertical and stemming material must be transported to the site. In these latter type of blasting operations ordinarily stemrning plugs are utilized, as for example, bagged particulate loose stemming materials, clay plugs and pleated asbestos plugs. Other tarnping means such as a plastic plug having flexible radial tins (US. 2,916,995) or a plug having a number of resilient members held in connement by a rupturable member (US. 2,449,645) are illustrative of devices which have been suggested for this use.

It is a principal object of the present invention to pro- 3,151,556 Patented Oct. 6, 1964 ICC contained in the internal passage, grips and tenaciously contacts the wall of a bore hole thereby resisting axial displacement in a direction toward the mouth of the bore hole. i

One embodiment of the tamping plug of this invention l is shown in FIGURES 142. This plug comprises a metal vide an improved tamping plug which gives a higher de- These and other objects and advantages will become apparent from the detailed description presented hereinafter when read in conjunction with the accompanying drawings.

In the drawings:

FIGURE l illustrates one embodiment of a tamping plug of the present invention.

FIGURE 2 is a top, planar View of the plug or FlG- URE l.

FIGURE 3 shows partly in section a second embodiment of a tamping plug of the present invention.

FIGURE 4 represents a loaded bore hole containing a tamping plug of the present invention prior to detonation.

FIGURE 5 illustrates the loaded bore hole of FEGURE 4 subsequent to press-fitting of the plug due to Primacord explosion and at start of the initiation of the base load.

FIGURE 6 shows the confining plug maintained in place as the explosive load depicted in FIGURE 4 undergoes detonation.

In general the tamping plug comprises a body of a metal in the form of substantially congruent and coaxial inverted conical frusturns readily forrnable by explosive energy which body has at least one passage substantially perpendicular to the parallel base and top plane surfaces to contain a high explosive whereby the plug upon expansion and deformation, from detonation of the explosive cylindrically shaped member 10 having a plurality of identical parallel, radial sloping walled shoulders 11 which form a series of inverted frustums. Two passages 12a- 12b extend through the plug parallel to the main axis of the plug being spaced diametrically opposite one another so as to pass through the plug near the outer edge of the smaller diametered plane surface of the frustum. Each of the holes 12a`-l2b are of a diameter to snugly accommodate a high energy detonating fuse or initiator such as a strand of Primacord.

FIGURE 3 depicts a plug wherein the bottom portion has been formed into a hollow frusto-conical form 13 and has a small passage 14 extending from the apex 15 of the truste-conical form 13 through the top 16 of the plug.

The frusto-conical form 13 can accommodate a conventional conical shape charge 1'7 and the passage 14 can hold an initiator 18 for this charge.

The tamping plug can be prepared from any metal which undergoes ready plastic deformation, or llow, under conditions used for explosive forming. Aluminum, lead and steel, for example, known to be readily formable by explosive forming techniques as Well as magnesium, copper and other metals and alloys are suitable for this application.

The plug can be fabricated by conventional techniques such as sand or permanent mold casting, machining from a billet, etc. Y

The plug diameter should be slightly less than the diameter of the bore hole in which it is to be employed, i.e.

having a maximum diameter of from about yg to about 1/4 inch less than that of the hole. This assures ready insertion and positioning of the plug in the bore hole and also provides for rni gripping of the wall of the bore hole upon explosive forming.

The depth and angle of cut of the shoulder indentations are not critical and are limited only in that the formed plug retains sutiicient structural strength when frictionally engaging the Wall of the bore hole to provide resistance towards blowing out of the plug from the bore hole upon detonation of the explosive charge.

The length of the plug `is not critical. However, as the bore diameter increases and/ or the size of Vthe explosive charge to be stemmed increases, the length of the tamping plug will be increased correspondingly in order to obtain the desired confinement of the load. Ordinarily the tamping plug will range from about 6 to about 36 inches in length or longer.

In use the plug ordinarily is inserted into a bore hole after the explosive charges and initiating means have been placed therein and is pressed into contact with the top of the charge. The plug, as used in a bore hole, has the bases of the frusturns facing the open end of the bore hole. With an embodiment as shown in FIGURES l and 2, two strands of a high energy fuse initiator,e.g. Prirnacord are passed through the passages 12a-12b. Conveniently, each of these strands can be knotted at the bottom to prevent them from being pulled from the plug while positioning in the bore hole. Alternatively if Primacord for example is being used directly as initiator for the explosive charge or to iire primer for the explosive load then the upper end of this fuse cord can be passed through one passage of plug prior to being connected to a tiring line. FIGURE 4 shows a plug having two passages therein where a Primacord initiating line for the load is passed through one channel in the plug and the other channel has a strand of fuse cord knotted at the bottom. To assure substantially simultaneous detonation of the two cards these are connected together as shown. As the Primacord is initiated, the metal plug is pressfitted, by the explosive energy from the fuse detonation, to tightly engage, by means of the edges of the protruding shoulders, the Wall of the bore hole and thereby give an unexpectedly high resistance to movement. This plug then provides an excellent degree of confinement for the explosive load when it is most needed during the early part of the explosive detonation. FIGURES 4, and 6, show in sequence the utility of the instant plug during detonation of an explosive charge in a bore hole.

The size of Primaeord, for most pressditting operations should be about 100 grains per foot or less in order to assure that undesirable fracturing or cracking of the plug does not occur. The number of strands to be used, i.e. the number of passages to be formed in the plug can vary from 1 up to about 4 or more depending primarily on the diameter of the bore hole. Ordinarily, the plug will contain one or two channels.

With a plug embodiment as shown in FIGURE 3, a shaped charge initiator can be positioned in the frustoconical shaped indentation 13. This plug thereby can serve as an initiator for the explosive load as well as be press-fitted into position without damage from the relatively small amount of lateral forces generated by initiation of the directed shaped charge. Alternatively, a strand of Primacord can be passed through this frustoconical shaped cavity and will give satisfactory press fitting of the plug upon initiation.

The etlectiveness of the coniining and retaining action of the tamping plug of the present invention is shown by the following examples.

A cylindrical block of aluminum about 8 inches long and 2. inches outside diameter was machined to have indented shoulders as shown in FIGURE 1. Two 1/1 inch diameter holes about 1 inch apart were drilled through the length of the plug and a strand of Primacord (100 grains per foot) passed through each hole. The plug with Primacord was placed inside a seamless steel pipe of about 21/ 6 inch inside diameter. The ends of the Primacord strands were connected to a common firing line. The Primacord was initiated and the aluminum plug was firmly press-fitted into the steel pipe.

The same test was repeated using a tamp plug having a single hole down through the center for one strand of Primacord. An excellent press tit resulted.

This same test was repeated using a tamping plug having three passages equidistantly spaced one from the other. Again a firm press-ht of the plug into the pipe was obtained.

A machined aluminum plug, about 21A inch outside diameter and about 8 inches long had two 14 inch passages drilled therethrough as described for the first exafd ample. Additionally the bottom portion of the plug was holiowed out in the form of a truste-conical form much the same as shown for the embodiment in FIGURE 3. Two strands of 1GO grains per foot Primacord were inserted through the two small passages and passed through the entire length of the plug. The plug was then placed inside of a 21/2 inch inside diameter stainless steel pipe. Detonation of the Primacord gave an excellent press t of the plug in the pipe.

ther modifications can be made in the present invention as will be apparent to one skilled in the art without departing from the spirit or scope thereof for it is understood that I limit myself only as deiined in the appended claims.

I claim:

1. A tamping plug for a bore hole comprising a body of a metal readily formable by explosive energy, said body being in the form of a series of substantially congruent and coaxial inverted conical frustums, said body having from l to about 4 small-diametered through passages extending over the length of the plug and being substantially perpendicular to the parallel ba-se and top plane surfaces of said plug, said passages being of such a diameter as to snugly accommodate a strand of high energy detonating fuse, the lower portion of the interior of said plug being expanded into the shape of a hollow, substantially frusto-conical form having its broad base at the bottom of said plug and its upper end contacting said through passages, said frusto-conical form accommodating a conical shaped charge detonator, said plug having a maximum diameter of less than that of said bore hole, said maximum diameter of said plug being such to assure ready insertion and positioning of the plug in a bore hole and provide for firm gripping of the Wall of the bore hole upon explosive forming, and, in combination with said plug a strand of a high energy detonating fuse for each of the sand small-diametered passages contained therein, each strand of said fuse passing through the entire length of a small-diametered passage of said plug and being snugly accommodated therein.

2. The tarnping plug as defined in claim 1 wherein there is a single, small-diametered through passage which snugly accommodates a ystrand of high energy detonating fuse, said passage extending down through the center of said plug and contacting the upper portion of said expanded frusto-conical, hollow form in the lower portion of said plug.

References Cited in the file of this patent UNITED STATES PATENTS 52,836 Felt Feb. 27, 1866 120,438 Holsey Oct. 31, 1871 971,264 Goodrow et al Sept. 27, 1910 1,587,664 McGraw June 8, 1926 2,656,891 Toelke Oct. 27, 1953 

1. A TAMPING PLUG FOR A BORE HOLE COMPRISING A BODY OF A METAL READILY FORMABLE BY EXPLOSIVE ENERGY, SAID BODY BEING IN THE FORM OF A SERIES OF SUBSTANTIALLY CONGRUENT AND COAXIAL INVERTED CONICAL FRUSTUMS, SAID BODY HAVING FROM 1 TO ABOUT 4 SMALL-DIAMETERED THROUGH PASSAGES EXTENDING OVER THE LENGTH OF THE PLUG AND BEING SUBSTANTIALLY PERPENDICULAR TO THE PARALLEL BASE AND TOP PLANE SURFACES OF SAID PLUG, SAID PASSAGES BEING OF SUCH A DIAMETER AS TO SNUGLY ACCOMMODATE A STRAND OF HIGH ENERGY DETONATING FUSE, THE LOWER PORTION OF THE INTERIOR OF SAID PLUG BEING EXPANDED INTO THE SHAPE OF A HOLLOW, SUBSTANTIALLY FRUSTO-CONICAL FROM HAVING ITS BROAD BASE AT THE BOTTOM OF SAID PLUG AND ITS UPPER END CONTACTING SAID THROUGH PASSAGES, SAID FRUSTO-CONICAL FROM ACCOMMODATING A CONICAL SHAPED CHARGE DETONATOR, SAID PLUG HAVING A MAXIMUM DIAMETER OF LESS THAN THAT OF SAID BORE HOLE, SAID MAXIMUM DIAMETER OF SAID PLUG BEING SUCH TO ASSURE READY INSERTION AND POSITIONING OF THE PLUG IN A BORE HOLE AND PROVIDE FOR FIRM GRIPPING OF THE WALL OF THE BORE HOLE UPON EXPLOSIVE FORMING, AND, IN COMBINATION WITH SAID PLUG A STRAND OF A HIGH ENERGY DETONATING FUSE FOR EACH OF THE SAND SMALL-DIAMETERED PASSAGES CONTAINED THEREIN, EACH STRAND OF SAID FUSE PASSING THROUGH THE ENTIRE LENGTH OF A SMALL-DIAMETERED PASSAGE OF SAID PLUG AND BEING SNUGLY ACCOMMODATED THEREIN. 